According to Saussure's 'dyadic' (two-part) model of the sign, each sign is composed of:
The relation between signifier and signified is arbitrary, nevertheless a community must have a sort of agreement to be able to communicate with each other. Where this does not happen there are different languages.
Concepts are an abstract construct. They are intended for referring to the mental image of something rather then the concrete object "in the world". As the mental image may not be constant for every person (see for example the Sapir-Whorf hypothesis), concepts are only used in discussions and the concrete reference to the real world may be argued about.
There is another dimension, illustrated by the semiotic triangle, it is the dimension of perception.
The semiotic triangle expresses the difference in the perception of the concept and the concept itself.
All: a term (definiendum) is defined.
The distinction between polysems and homonyms is not easy in some cases. When in doubt they are distinguished by their etymology (if they are derived from the same word they are polysems, if they are derived from two different words they are homonyms).
| Word level | Sentence level |
| Synonymy | Paraphrase |
| Antonymy | Contradiction |
| Polysemy | |
| Homonymy | |
| entailment |